It proved to be a case of ‘easier done than said’ for the thieves who stole seven masterpieces worth millions of dollars from the Dutch gallery in mid October. The police say security at Rotterdam's Kunsthal was not up to scratch.

­The art gallery says the thieves were able to swiftly snatch the artworks by Matisse, Monet and Picasso in an overnight burglary after an alarm briefly deactivated a rear door’s electronic lock.

Although the door had mechanical locks, the thieves managed to break inside, the Dutch museum explained. Images caught on camera revealed they entered and left within 120 seconds, ahead of the police who arrived five minutes after the alarm sounded.

The investigators have posted a YouTube video showing two masked individuals slipping inside and coming out with their bags filled. The theft is said to be one of the largest in the Netherlands.

The police said they have had more than 60 tips in connection with the burglary on October 16, when thieves took advantage of the electronic lock system, which opened to comply with fire safety regulations, The New York Times reported.

“We must always make the trade-offs between safety and security,” the Director of the museum, Emily Ansenk, explained in a statement.

The pictures were part of an exhibition which opened in early October as part of the gallery’s 20th anniversary celebrations. The works belonged to the Triton Foundation which holds pieces by the most important and influential artists of the late nineteenth century to the present day.